Field
The invention relates to a polyaxial bone anchoring device with an enlarged pivot angle. The bone anchoring device includes a bone anchoring element for anchoring in a bone or a vertebra, a receiving part for coupling the bone anchoring element to a stabilization element such as a spinal rod, where the bone anchoring element is pivotable in the receiving part and can be pivoted out of a central axis with an enlarged pivot angle. The orientation of the enlarged pivot angle may be selectable within a range of 360° around the central axis and may be automatically achieved by pivoting the receiving part relative to the bone anchoring element. The receiving part can be mounted to the bone anchoring element in situ when the bone anchoring element has been implanted into the bone.
Description of Related Art
A polyaxial bone anchoring device with an enlarged pivot angle that is selectable within a range of 360° around the central axis is described in US 2012/0136395 A1. The polyaxial bone anchoring device includes a sleeve-like insert piece that is configured to be positioned around a portion of the head of the bone anchoring element and to pivot in the receiving part. When the head, the insert piece and a pressure member are arranged in the receiving part, the insert piece is tiltable with respect to the longitudinal axis of the receiving part and with respect to a longitudinal axis of the anchoring element, and the anchoring element and the insert piece can be locked at respective angles relative to the longitudinal axis of the receiving part by exerting pressure with the pressure member onto the head.
U.S. Pat. No. 7,625,396 B2 describes a polyaxial bone screw assembly that includes a threaded shank body having an upper capture structure, a head and a multi-piece retainer articulation structure. The head has a U-shaped cradle defining a channel for receiving a spinal fixation or stabilization longitudinal connection member. The geometry of the retainer structure pieces corresponds and cooperates with the external geometry of the capture structure to frictionally envelop the retainer structure between the capture structure and an internal surface defining a cavity of the head. The retainer structure includes a substantially spherical surface that mates with the internal surface of the head, providing a ball joint, enabling the head to be disposed at an angle relative to the shank body. Typically, the head and the retainer structure are assembled on the shank before implanting the shank body into the vertebra.